The invention relates to a method for detecting a noise signal power of a power line. The method comprises the following steps: step a, on the basis of a frequency difference between a power frequencyand that of a carrier signal needing to be tested, carrying out coupling of a power frequency signal and a tested signal; step b, transmitting a coupled power line signal to a band-pass filtering unit; step c, processing the filtered signal by using a carrier signal power testing unit; step d, generating a local oscillator signal needed by a mixing unit in the carrier signal power testing unit byusing a program-controlled local oscillator unit; step e, transmitting a filtered intermediate-frequency signal to an AD sampling unit for detection; and step f, sending AD data generated by the AD sampling unit to a DSP unit for FFT operation. With the obtained power information, noise time domain information, and frequency domain information of the noise, graphic displaying of waveform data andspectrum data of the collected current power line signal is realized and the noise signal in the power line is analyzed deeply and conveniently, so that the accuracy of terminal communication is enhanced and reliability is improved; and targeted advice is provided for selection of a terminal product.